Godspeed You! Black Emperor have returned with their first album in 10 years, springing it on the world at a gig in Boston on Monday. The first anyone outside Godspeed's camp knew of the record was when fans approached the merch table at the Orpheum theatre and saw vinyl copies of Allelujah! Don't Bend! Ascend! for sale.

The band will be talking about their new album in an exclusive interview in next week's G2 Film & music, and the Guardian will be streaming the album in full.

It has been a little over two years since Godspeed returned to the spotlight, reforming to curate the All Tomorrow's Parties festival. The hugely influential post-rock ensemble have toured persistently since then, criss-crossing the US, visiting Europe and even playing outdoor festivals like Coachella and Pitchfork. Despite these appearances, the reclusive musicians revealed almost nothing about recording; percussionist Bruce Cawdron was the only one to admit it was happening, in May 2011.

Then abruptly on Monday night, Allelujah! was out. Sort of. Although the record won't be properly released until 15 October, the band has started selling it at gigs. It is also available for pre-order – although Godspeed's longtime label, Constellation Records, has run out of vinyl. "We sincerely and strongly encourage you to support independent music retailers by buying the album when it is in stores or appears on other mail-order sites," they said.

On vinyl, the album consists of just two songs, each more than 20 minutes long. Both are old compositions, recorded recently in Montreal. An accompanying 7in includes two drone tracks. Although the album artwork could have been part of a Godspeed release circa 2000, full of urban decay and melted celluloid, the songs include references to Montreal's recent protests, the so-called Maple spring. One song is titled Strung Like Lights at Thee Printemps Érable, and another incorporates a recording of the clanging pots and pans of a summer "casserole".